In test_no_kmem_bypass(), delta (stored_pages * page_size - zswapped) is
checked against stored_pages * page_size / 4 to verify that the pages
pushed to zswap belong to the test memory cgroup.
Due to slight stat update timing differences, delta can evaluate to a small
negative number (e.g. -5MB out of 1GB). Because delta was declared as a
signed int and stored_pages is an unsigned size_t, C's usual arithmetic
conversions implicitly promote a negative delta to a large unsigned 64-bit
integer, causing `delta < stored_pages * page_size / 4` to falsely evaluate
to 0 and fail the test.
Fix this by declaring delta and max_delta as signed 64-bit values (s64),
explicitly casting stored_pages, and comparing against a signed threshold,
ensuring negative deltas correctly evaluate to true.
Fixes: a549f9f31561 ("selftests: cgroup: add test_zswap with no kmem bypass
test")
Signed-off-by: Wilson Felipe Pereira <[email protected]>
---
tools/testing/selftests/cgroup/test_zswap.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/tools/testing/selftests/cgroup/test_zswap.c
b/tools/testing/selftests/cgroup/test_zswap.c
index f4ee440b3c66..6e7ee11bc97a 100644
--- a/tools/testing/selftests/cgroup/test_zswap.c
+++ b/tools/testing/selftests/cgroup/test_zswap.c
@@ -632,11 +632,12 @@ static int test_no_kmem_bypass(const char *root)
break;
/* If memory was pushed to zswap, verify it belongs to memcg */
if (stored_pages > stored_pages_threshold) {
- s64 zswapped = cg_read_key_s64(test_group,
"memory.stat", "zswapped ");
- int delta = stored_pages * page_size - zswapped;
- int result_ok = delta < stored_pages * page_size / 4;
+ s64 zswapped = cg_read_key_s64(
+ test_group, "memory.stat", "zswapped ");
+ s64 delta = (s64)stored_pages * page_size - zswapped;
+ s64 max_delta = (s64)stored_pages * page_size / 4;
- ret = result_ok ? KSFT_PASS : KSFT_FAIL;
+ ret = (delta < max_delta) ? KSFT_PASS : KSFT_FAIL;
break;
}
}
--
2.55.0.979.g7e5102b832-goog
